had my spark plugs out to check condition and i thought, "why the hell not?" they had light ash deposits, but were otherwise clean and in GC. than i busted out the piston comp tester.

i was really happy to see the rear rotor put up ~122 psi after a few sweeps and the front one was ~128 psi. i don't know how accurate this is compared to a rotary compression tester, but the numbers sound good to me.



nice even pulses with the valve in. no surprise really, she rips after warming up.

12k on a full rebuild by yours truly, with used s5 rotor housings and rotors. replaced internals with atkins parts. i also premix TCW-3 128/1 ratio and always have on the engine.

 

If you used it correctly those are good numbers for a rebuilt motor. Was it warm when you tested? Want to rebuild mine?

 

well i used the top plug holes instead of the bottom ones and didn't hold the throttle open... it had been cooling down for several hours.

yeah, crate it up and ship it down. i'll get on it as soon as i finish my REW and my physics homework

 

It's perfectly accurate, except it will only tell you the best of the 3 rotor faces. If one face is bad (or worse than the other 2), the piston compression tester won't tell you.

 

I tested mine and got 60psi on both rotors!!!!!!!!!!! Thats good right? :P

 

If you want real numbers for each face, try this

https://www.rx7club.com/showthread.php?t=585982

 

my compliments. that a great idea and i hope you sell quite a few.

 

Hmm, you should be using the leading (bottom) holes, and holding the throttle wide open to be getting totally accurate readings. And to the people posting above, a piston compression tester with the valve removed (like he said he did) will show you seperate faces..I don't know where you get this "it won't" idea...


Those numbers sound too good to be true, especially on a rebuild w/ used housings..I've never seen more than 125, even on a reman O.o

 

Wrong.
Mazda spec is with BOTH trailing spark plugs pulled and using one of the trailing holes for the compression tester.


-Ted

 

well, i figure that holding the throttle would actually give me better readings because the engine would be working against less vacuum pressure.

and the trailing plug holes i tested on are smaller than the leading, but i have no idea how that would affect things the reading. probably not at all... except again, the engine would have a harder time spinning because it would be harder to force pressure out of the open trailing hole because of it's diameter.


well, the housings were nearly perfect s5 pieces. even so, i know it shouldn't be quite that high. either way it is a good indication that i am making proper compression, so i'm happy with it, you know?

just because mazda didn't pay me to build it doesn't mean it can't be as good as or better than someone else's work.



.

 

The rotor sweep in the combustion chamber hits the trailing hole first.
Mazda made the hole small so that to minimize compression leaking into the trailing hole.
On very sensitive compression testers, you can lose about 5% of compression if you're using the leading versus the trailing.
This is why Mazda uses the trailing hole.


-Ted